1. Technical Field of the Invention
The invention relates to a composition comprising, in a physiologically acceptable medium, at least one retinoid, dispersed benzoyl peroxide and at least one pH-independent gelling agent.
2. Description of the Prior Art
The use of several classes of active principles is a therapeutic tool that is frequently employed, especially for treating dermatological disorders.
Specifically, it is known practice in the treatment of dermatitis to use corticosteroids such as, for example, hydrocortisone, miconazole or betamethasone valerate, antihistamines (e.g., mizolastine) and/or keratolytic agents, for instance salicylic acid. Various antifungal agents, for instance allylamine derivatives, triazoles, antibacterial agents or antimicrobial agents such as, for example, antibiotics, quinolones and imidazoles, are also conventionally combined in the treatment of dermatological diseases. Peroxides, D vitamins and retinoids are also described for the topical treatment of various pathologies associated with the skin or mucous membranes, in particular acne.
The combination of several local treatments (antibiotics, retinoids, peroxides and zinc) is also used in dermatology to increase the efficacy of the active principles and to reduce their toxicity (Cunliffe W. J., J. Dermatol, Treat., 2000, 11 (suppl2), pp. 13-14).
The multiple application of various dermatological products may be relatively burdensome and restricting for the patient.
The value in seeking to obtain a novel treatment that is effective on dermatological complaints in a stable composition offering good cosmetic utility, allowing a single application and a utilization that the patient finds pleasant, may thus be appreciated.
Among this panoply of treatments proposed to a person skilled in the art, there was nothing to encourage him to combine, in the same composition, benzoyl peroxide and a retinoid.
However, formulating such a composition poses several problems.
Firstly, the efficacy of benzoyl peroxide is associated with its decomposition when it is placed in contact with the skin. Specifically, it is the oxidizing properties of the free radicals produced during this decomposition that lead to the desired effect. Thus, in order to maintain the optimum efficacy of benzoyl peroxide, it is important to prevent its decomposition before use, i.e., during storage.
Benzoyl peroxide is an unstable chemical compound, making it difficult to formulate it in finished products.
The solubility and stability of benzoyl peroxide were studied by Chellquist at al., in ethanol, propylene glycol and various mixtures of polyethylene glycol 400 (PEG 400) and water (Chellquist E. M. and Gorman W. G., Pharm. Res., 1992, Vol 9: 1341-1346). Benzoyl peroxide is particularly soluble in PEG 400 and ethanol, as shown in the following table:
Benzoyl peroxideSolventsolubility (mg/g)PEG 40039.6Ethanol17.9Propylene glycol2.95Propylene glycol/water (75:25)0.36Glycerol0.15Water0.000155
The said document moreover states that the stability of benzoyl peroxide is greatly influenced by the chemical composition of the formulation and by storage temperature. Benzoyl peroxide is extremely reactive and degrades in solution at low temperature on account of the instability of its peroxide bond. The authors thus state that benzoyl peroxide in solution degrades more or less quickly in all the solvents studied as a function of the type of solvent and of its concentration.
The degradation times for benzoyl peroxide in PEG 400 (0.5 mg/g), in ethanol and in propylene glycol are, respectively, 1.4, 29 and 53 days at 40° C.
Such a degradation does not allow the preparation of a product intended for sale.
It is moreover known that benzoyl peroxide is more stable in water and propylene glycol when it is in suspension (i.e., in dispersed form), since it is not degraded after storage for 90 days in these solvents. Thus, in order to limit the problem of rapid instability of benzoyl peroxide in solution, it has been found to be advantageous to formulate benzoyl peroxide in dispersed form. However, this type of formulation is not entirely satisfactory since degradation of the benzoyl peroxide in the finished product is still observed.
Another difficulty to be overcome in preparation of a composition comprising both benzoyl peroxide and a retinoid is that most retinoids are particularly sensitive to natural oxidation, to visible light and to ultraviolet light, and, since benzoyl peroxide is a strong oxidizing agent, the chemical compatibility of these compounds in the same formulation poses numerous problems in terms of physical and chemical stability.
A study of the stability of two retinoids was performed by combining two commercial products, one containing a retinoid (tretinoin or adapalene) and the second based on benzoyl peroxide (B. Martin et al., Br. J. Dermatol. (1998) 139, (suppl. 52), 8-11). The presence of the formulation based on benzoyl peroxide results in very rapid degradation of the oxidation-sensitive retinoids: it is measured that 50% of the tretinoin is degraded in 2 hours, and 95% in 24 hours. In the composition in which the retinoid is adapalene, no degradation of the adapalene was measured over 24 hours. This study confirms that benzoyl peroxide becomes degraded and degrades oxidation-sensitive retinoids over time, gradually releasing benzoic acid into the finished products. In contrast, no indication is given regarding the physical stability of the two compositions placed in contact, or regarding the therapeutic activity that may finally be obtained by combining the two active principles in the same composition. There was no encouragement for combining these two active agents in order to obtain a stable composition of gel type, given that it was commonly known that the presence of benzoyl peroxide chemically and physically destabilized this type of composition.
Now, it is clear that the degradation of benzoyl peroxide and retinoids is not desirable since it impairs the efficacy of the composition containing them.
Moreover, a finished product, in particular when it is a pharmaceutical or cosmetic composition, must maintain throughout its shelf life precise physicochemical criteria for ensuring its pharmaceutical or cosmetic quality, respectively. Among these criteria, it is necessary for the rheological properties to be maintained. They define the behavior and texture of the composition during application, but also the active principle's release properties [1998 SFSTP Commission Report] and the homogeneity of the product when the active principles are present therein in dispersed form.
In particular, the formulation of benzoyl peroxide and of a retinoid in gel form is advantageous for topical treatments, such as the treatment of acne, since it especially avoids a greasy feel being left on the skin.
Another difficulty to be overcome in preparing a composition especially comprising benzoyl peroxide, when it is in gel form, is that the gelling agents are destabilized by the benzoic acid released during the degradation of the benzoyl peroxide.
Specifically, the thickeners most commonly used for formulating these compositions with benzoyl peroxide are acrylic acid polymers (Carbomer) and celluloses alone or combined with silicates.
Now, the use of carbomers in compositions of aqueous gel type does not give good results in terms of chemical stability of the benzoyl peroxide or in terms of rheological stability. As described by Bollinger (Bollinger, Journal of Pharmaceutical Science, 1977, vol 5), it has been observed that from 5% to 20% benzoyl peroxide is lost after 2 months at 40° C. depending on the neutralizer of the carbomer used. Furthermore, the release of benzoic acid results in depolymerization of the carbomers, leading to a drop in viscosity which may result in phase separation. In other gels consisting of a mixture of hydroxypropyl-cellulose and aluminum magnesium silicate, a drop in viscosity over time is also observed, resulting in sedimentation of the active agents as a suspension and heterogeneity of the dispersion in the finished product.
This instability of benzoyl peroxide gels impairs their efficacy and their cosmetic utility.
There is thus still a need for a physically stable gelled composition containing benzoyl peroxide and a retinoid.